1. Field of the Invention
The present invention relates to a piezoelectric oscillator unit, and more particularly, to a surface-mounted piezoelectric oscillator unit utilizing a quartz vibrator to provide a standard frequency used in a portable terminal.
2. Description of the Related Art
FIG. 6 shows a conventional quartz oscillator unit 31 using a surface-mounted quartz vibrator package. In this quartz oscillator unit 31, a surface-mounted quartz vibrator package 33 is mounted on the top surface of a flat circuit substrate 32, electrodes provided on the bottom surface of the quartz vibrator package 33 are electrically connected to electrode pads on the circuit substrate 32 by reflow soldering, and the quartz vibrator package 33 is mechanically fixed to the circuit substrate 32 with solder 34. Circuit components 35 and 36 defining an oscillating circuit, and a temperature compensation circuit are mounted on the circuit substrate 32, a shielding case 37 is provided on the circuit substrate 32 to cover the quartz vibrator package 33 and the circuit components 35 and 36, and the shielding case 37 is soldered to the circuit substrate 32 with solder 38.
In the quartz oscillator unit 31 having the structure described above, however, the quartz vibrator package 33 and the shielding case 37 are connected to the circuit substrate 32 mechanically and electrically only by solder, and hence, when attempting to solder the quartz oscillator unit 31 to a printed-circuit board by reflow soldering or flow soldering, the solder 34 which has bonded the quartz vibrator package 33 to the circuit substrate 32 melts in the process of reflow soldering or flow soldering, such that the quartz vibrator package 33 may be lifted from the circuit substrate 32 or may slide thereon. Also, when reflow soldering or flow soldering the printed-circuit substrate 32 while laying the circuit substrate face down with the quartz oscillator unit 31 at the lower side, the quartz vibrator package 33 may fall off from the circuit substrate 32 due to vibrations occurring during reflow soldering once the solder 34 melts.
Furthermore, when the quartz oscillator unit 31 is reflow soldered or flow soldered, not only the quartz vibrator package 33, but also the shielding case 37, may lift off of the circuit substrate 32, move thereon, or fall off of the circuit substrate 32.
Moreover, not only in the case where the quartz oscillator unit 31 is mounted, but also in the case where the equipment printed-circuit substrate on which the quartz oscillator unit 31 has been mounted is repaired, when the equipment printed-circuit substrate is placed on a heating plate to melt the solder, and the quartz oscillator unit 31 is removed from the equipment printed-circuit substrate, the heat of the melted solder and that of the heating plate causes the quartz vibrator package 33 and/or the shielding case 37 to lift or detach from the circuit substrate 32.
In recent years, with the miniaturization of quartz oscillator units, circuit substrates have been miniaturized to a size comparable to that of the quartz vibrator package, and consequently the space for soldering the shielding case to the circuit substrate in the quartz oscillator unit is greatly reduced or eliminated. A quartz oscillator unit having no shielding case has been introduced, and which uses only the shielding effect of the quartz vibrator package itself. In such a quartz oscillator unit, since the quartz vibrator package thereof is not covered with a shielding case, the likelihood that the quartz vibrator package will lift from or fall off the circuit substrate due to the heat in the reflow soldering and the heat of the heating plate is greatly increased.
To prevent such problems, high-temperature solder may be used to fix the quartz vibrator package and the shielding case to the circuit substrate by reflow soldering. The high-temperature solder is, however, difficult to handle, because the use of the high-temperature solder requires a higher heating temperature reflow furnace which can produce adverse effects on semiconductor components.
To overcome the above-described problems, preferred embodiments of the present invention provide a piezoelectric oscillator unit which maintains the adhesive force of the vibrator package with respect to the circuit substrate even when the solder connecting the quartz vibrator package to the circuit substrate melts, that is, a piezoelectric oscillator unit which is capable of preventing the vibrator package from lifting from or falling off the circuit substrate even if the vibrator package is subjected to heating when the piezoelectric oscillator unit is mounted or repaired.
A first preferred embodiment of the present invention provides a piezoelectric oscillator unit including a vibrator package housing a piezoelectric component which is overlaid on a circuit substrate on which an oscillating circuit is mounted, and in which the electrodes provided on the top surface of the circuit substrate and the electrodes provided on the bottom surface of the vibrator package are bonded together using a brazing material such as solder, wherein the circuit substrate and the vibrator package are bonded together via an adhesive.
In the piezoelectric oscillator unit in accordance with the first preferred embodiment of the present invention, since the vibrator package housing the piezoelectric member (a quartz member for example) is overlaid on the circuit substrate, and the vibrator package and the circuit substrate are bonded together using an adhesive such as a thermosetting adhesive, the adhesive force between the vibrator package and the circuit substrate is maintained even when the solder bonding the quartz vibrator package to the circuit substrate is melted by the heat of a reflow furnace, a flow soldering device, a heating plate for repair, or other heat sources. This prevents the vibrator package from developing defects such as lifting from or falling off the circuit substrate in the mounting or repairing process.
Also, since the adhesion area between the vibrator package and the circuit substrate is greatly increased, the transverse rupture strength of the piezoelectric oscillator unit is greatly enhanced. Among the overlapping surfaces of the quartz vibrator package and the circuit substrate, the bonding surfaces to be bonded by an adhesive include the entire surfaces except for the electrode portions, or portions thereof.
A second preferred embodiment of the present invention provides a piezoelectric oscillator unit including a vibrator package housing a piezoelectric member which is overlaid on a circuit substrate on which an oscillating circuit is mounted, and in which the electrodes provided on the top surface of the circuit substrate and the electrodes provided on the bottom surface of the vibrator package are bonded together using a brazing material such as solder, wherein the vibrator package is covered with a shielding case, the vibrator package is held by the shielding case, and the shielding case is adhered to the circuit substrate by an adhesive.
In the piezoelectric oscillator unit in accordance with the second preferred embodiment of the present invention, since the shielding case covering the vibrator package is adhered to the circuit substrate by an adhesive such as a thermosetting adhesive, and the vibrator package is held by the shielding case, the vibrator package is retained by the shielding case, even when the solder bonding the quartz vibrator package to the circuit substrate is melted by the heat of are flow furnace, a flow soldering device, a heating plate for repair, or other heat source. This prevents the vibrator package from developing defects such as lifting from or falling off the circuit substrate.
Preferably, in the piezoelectric oscillator unit in accordance with the second preferred embodiment of the present invention, each of a plurality of protrusions provided on the shielding case is inserted into a corresponding hole provided in the circuit substrate, and each of the protrusions on the shielding case is fixed in the corresponding hole in the circuit substrate by the adhesive, which is provided in each of the holes.
As described above, since the piezoelectric oscillator unit is arranged such that each of the protrusions on the shielding case is inserted into one of the holes in the circuit substrate, the shielding case is accurately positioned even when the area of the circuit substrate is small. Further, since each of the protrusions is fixed by the adhesive provided in one of the holes, the shielding case is securely fixed to the circuit substrate.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the detailed description of preferred embodiments below with reference to the attached drawings.